An Organic Light-Emitting Diode (OLED) display screen has been put in the list of next generation display technologies which have wide development prospects, due to advantages such as thinness, lightness, wide viewing angle, active light emitting, continuous and adjustable light-emitting color, low cost, fast response speed, low energy consumption, low driving voltage, wide working temperature range, simple production process, high light-emitting efficiency, and flexible display and so on.
An OLED device is generally formed on a substrate by an evaporation process, which refers to that an evaporation material is heated under a certain vacuum condition, the evaporation material is melted (or sublimated) into vapor composed of atoms, molecules or atomic groups, then the vapor is congealed on a surface of the substrate to form a film, so as to form a functional layer of the OLED device. The evaporation process can be divided into point source evaporation and line source evaporation according to types of an evaporation source (a heating device of the evaporation material). The development of point source evaporation technology is relatively mature, and mass production has been achieved on a production line.
The evaporation material is expensive and low in utilizing rate, because a path for evaporation gas molecules to overflow from a crucible to the substrate in a high-vacuum environment is long. Thus, a proportion of evaporation gas molecules flying to the surface of the substrate and deposited on the surface of the substrate is not greater than 5%, and most of the evaporation material is deposited on inner wall of a cavity, which, on one hand, pollutes the cavity, and on the other hand, affects a vacuum degree of the cavity.